I am okay with moving to GitLab. I think this platform has more benefits than most out there right now, including GitHub.
Regardless, I am in favor of waiting so the projects can be finished. Despite GitLab having lots of tools to help people migrate to their platform and what-not, they are a bit overloaded right now and moving 300+ repositories now will take days or even weeks. It will be a complicated task and if we do it now it will take longer than we can take.
The strategy should be planned in a future meeting by the devs and decide on what is the best course of action to minimize recursions and find the best occasion to make it happen.